This application claims the priority benefit of Taiwan application serial no. 89107668, filed Apr. 24, 2000.
1. Field of Invention
The present invention relates to a switch. More particularly, the present invention relates to a mirror layout of an optical switch.
2. Description of Related Art
In optical fiber communication, an optical switch that employs a micro-electromechanical system (MEMS) has become an important component for relaying optical signals. A conventional optical switch has a one-to-one crossbar configuration. FIG. 1 is a schematic layout of the mirrors inside a conventional one-to-one crossbar optical switch.
As shown in FIG. 1, the optical switch 10, such as 4-by-4 optical switch, consists of a set of 16 reflecting mirrors Sij arranged into a 4-by-4 matrix configuration where i and j are integers that range from 1 to 4 respectively. An incident beam enters the optical switch from the left in one of the four input optical paths I1, I2, I3 and I4. After an internal reflection takes place somewhere inside the optical switch, the incident beam leaves the optical switch 10 from the bottom out of one of the four output optical paths O1, O2, O3 and O4. All the reflecting mirrors Sij can be individually raised or lowered. If the reflecting mirror S11 is raised while all the other mirrors are lowered, the incident beam that enters the optical switch 10 through input optical path I1 will leave via output optical path O1. Similarly, the incident light beam from the optical path I1 can be redirected to output optical paths O2, O3 and O4 by raising the mirrors m12, m13 and m14 while lowering the other mirrors, respectively. To carry out optical switching, such as redirecting the incident beam from input optical path I3 to output optical path O4, the reflecting mirror m34 can be raised while all the other mirrors, including S31, S32, S33 and S44, are all lowered.
The raising and lowering of reflecting mirrors Sij is normally triggered by a control logic circuit (not shown in FIG. 1). By raising and lowering the reflecting mirrors in various combinations, the incident beam can be reflected by an internal mirror to any desired output optical path of the optical switch. Hence, switching multiple light sources to multiple destinations is available. Each row and each column must have one reflecting mirror raised depending upon the incoming-to-outgoing light path. The raising and lowering of the reflecting mirrors within the optical switch is normally controlled by logical circuits. In general, the reflecting mirrors are moved and controlled by a micro-electromechanical technology, existing in exsitent patents or papers.
The aforementioned crossbar arrangement of reflecting mirrors has one major drawback. As the switching optical paths increase, the number of reflecting mirrors inside the optical switch increases as the square of the number of input or output paths. However, putting too many reflecting mirrors inside an optical switch may lower production yield and reliability.
Aside from the one-to-one crossbar configuration, an optical switch that uses double-sided reflecting mirrors 24, 32, 34, 36 and 38 and fixed mirrors 22a, 22b is proposed in U.S. Pat. No. 4,815,827, which is shown in FIG. 2. Although multiple reflections are used to carry out the optical switching, the prior art structure still has to use many reflecting mirrors.
FIG. 2 is a schematic diagram showing an optical switch that utilizes multiple reflections. As shown in FIG. 2, the optical switch 20 includes two single-sided reflecting mirrors 22a and 22b. The reflecting mirrors 22a and 22b are parallel to each other with their reflecting surfaces facing each other. Symmetrically positioned between the two reflecting mirrors 22a and 22b is an axis Y. Along the axis Y are twelve double-sided equidistantly spaced reflecting mirrors 24. In addition, double-sided reflecting mirrors 32, 34, 36 and 38 are positioned between the reflecting mirrors 22a and 22b according to desired light-reflecting and switching conditions. With this structure, a 4-by-4 configuration switching can be achieved between input optical paths I1, I2, I3 and I4 and output optical paths O1, O2, O3 and O4. However, the structure requires 16 double-sided mirrors altogether in addition to the two fixed mirrors 22a and 22b. Hence, other than equalizing the propagation distance in each of the optical routes, the number of reflecting mirrors is the same as the crossbar structure shown in FIG. 1, not reducing the number of the doubled-side reflecting mirrors.
In short, the one-by-one crossbar configuration inside the optical switch in FIG. 1 uses the largest number of reflecting mirrors. When a micro-electromechanical system is incorporated into the optical switch, the area needed to form the optical switch is proportional to the number of reflecting mirrors. In other words, the area required to form the optical switch is large when the one-by-one crossbar configuration is used. Hence, system production yield, system reliability and production cost all will be affected.
If there exists a systematic method for the mirror layout of the multi-level optical switch, the manufacturing area can be reduced considerably. In addition, when the number of reflecting mirrors is reduced, circuits for driving the reflecting mirror are correspondingly reduced, and possible errors, chance of failures and power consumption of the optical switch are all lowered.
Accordingly, one object of the present invention is to provide a method for laying out the reflecting mirrors of a multi-level optical switch so that the switch uses a less number of reflecting mirrors and occupies less area.
A second object of the invention is to provide a method that utilizes Batcher""s odd-even merging network theory to arrange the reflecting mirrors inside a multi-level optical switch.
A third object of the invention is to provide a method that utilizes Batcher""s odd-even merging network theory to arrange the reflecting mirrors inside a optical switch with power of 2 input/output optical paths.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method for laying out the reflecting mirrors of a multi-level optical switch. The multi-level optical switch includes a plurality of input terminals and a plurality of output terminals. A first fixed single-sided reflecting mirror and a second fixed single-sided reflecting mirror are installed inside the multi-level optical switch. The reflecting surfaces of the first and the second fixed single-sided reflecting mirrors face each other and are parallel to each other. The area between the first and the second fixed reflecting mirrors form the layout region for the double-sided reflecting mirrors. The layout region has a plurality of optical path cross-points capable of separating the incoming light rays into either an odd optical group or an even optical group. Various incoming light paths of the odd optical group are assimilated using a network-switching algorithm to compute a plurality of optical path cross-points. Similarly, various incoming light paths of the even optical group are assimilated using a network-switching algorithm to compute a plurality of optical path cross-points. A double-reflecting mirror is positioned at the optical cross-point on the rectangular matrix inside the multi-level optical switch. The location for the double-reflecting mirror is found by the network-switching algorithm. The double-reflecting mirror can reflect light or let the light pass therethrough.
The network-switching algorithm includes a Batcher""s odd-even merging network that uses a 2-by-2 comparator as the basic unit. Hence, the layout of any N (positive and with power of two) level optical switch can be computed using the Batcher""s odd-even merging network method.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.